Gross coccidial lesion scores appear to predict microscores
Microscopic oocyst counts of intestinal scrapings, also called microscores, are often investigated along with bodyweight gain and gross intestinal lesion scores as part of anticoccidial sensitivity tests (AST), which are conducted to determine the efficacy of anticoccidials against Eimeria field isolates, Barrios said.
In a study, Barrios and colleagues from the university, with support from Zoetis Inc., determined the correlation between broiler bodyweight, gross lesion score and microscores as part of three ASTs.
There were 288 chicks per AST. On day 13 of age, investigators gave each group one of 10 anticoccidials including lasalocid, salinomycin, monensin and narasin. For controls, they had one group that was not medicated or infected and another group that was not medicated but infected.
On day 15, the researchers challenged chicks in the medicated groups and the unmedicated control group with Eimeria oocysts from the field. One day 21, they weighed the birds and classified gross lesion scores and microscores from Eimeria maxima using the 0 to 4 Johnson and Reid evaluation method.
Investigators found no correlation between microscores and bodyweight gain, but there was a positive correlation between gross lesions and microscores (p = 0.004). There was also an interaction between microscore and isolate, which may be due to the differing pathogenicity of the challenge isolates. This finding indicates that the significance of the correlation between microscores and gross lesions may depend on the Eimeria strain, Barrios said.
1 Barrios M, et al. Establishing the correlation between broiler body weight gain, gross lesion score, and microscores in three anticoccidial sensitivity tests. 2015 International Poultry Scientific Forum abstracts.